1. Field of the Invention
This invention relates to a load sensor using a material which ohmic resistance changes according to load acting thereon, a temperature compensation method for the load sensor and a manufacturing method of the load sensor.
2. Discussion of the Background
Semiconductors such as silicon or functional ceramics are known as materials whose ohmic resistance changes according to load acting thereon. The ohmic resistance of these materials changes according to not only the load but also temperature. Therefore, some temperature compensation is needed in order to use these materials for a detecting element of a load sensor. On that account, a first conventional load sensor adopts a load detecting element which the ohmic resistance changes more greatly according to the load than according to the temperature. A second conventional load sensor has a temperature sensor such as thermistor and a compensation circuit which compensates output from the detecting element according to the temperature measured by the temperature sensor. A third conventional load sensor has a compensation element which has similar temperature characteristic with a load detecting element, and compensates output from the detecting element by the compensation element. Japanese Laid Open Patent Publication No. 5-118932 discloses one example of the third conventional load sensor. The load sensor disclosed by the publication uses amorphous-magnetism-alloy for a load detecting element. The amorphous-magnetism-alloy is coiled around one part which load acts on and another part which load does not act on respectively. Variation of magnetic permeability of each amorphous-magnetism-alloy is detected by a coil. And so, a temperature characteristic of the magnetic permeability of the amorphous-magnetism-alloy is compensated by difference of the magnetic permeability of both amorphous-magnetism-alloy.
However, in the first conventional load sensor, it is difficult to get such small temperature characteristic material for the detecting element. Even if it can be gotten, since the temperature characteristic of the material is even small but not zero, some detection error of the load sensor causes in a circumstance of huge temperature variation. In the second conventional load sensor, if the temperature characteristic of the material is a linear function, the compensation circuit can compensate the output from the detecting element. However, when the temperature characteristic of the material is a non-linear function, the compensation circuit can not compensate the output correctly. In the third conventional load sensor, it is difficult to get such similar temperature characteristic element for the compensation element. Even if it can be gotten, there is a problem that temperature difference between the load detecting element and the compensation element causes because of difference of installation locations or forms of the load detecting element and the compensation element.